Seals for the gas hoods of sintering machines



July 3, 1962 H. RAUSCH ETAL 3,042,390

SEALS FOR THE GAS x-xoons 0F SINTERING MACHINES Filed July 11, 1958 rrom e s United States Patent 3,042,390 SEALS FOR THE GAS HOODS OF SINTERING MACHINES Hans Rausch, Oberursel (Taunus), and Kurt Meyer,

Frankfurt am Main, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Filed July 11, 1958, Ser. No. 747,990 1 Claim. (Cl. 266-21) This invention relates to seals for the gas hoods of sintering machines.

It is well known that the use of sintering machines is not limited to sintering, roasting, and heating processes. Sintering machines are also used for carrying out reactions in which gases are evolved or consumed. In the latter case, it is often desirable that the composition of the gaseous atmosphere under the gas hood above the sintering band be capable of being exactly controlled. It is also desirable to be able to adjust the absolute gas pressure under the gas hood. For both these purposes the existence of an efiicient seal between the stationary gas hood and the travelling sintering band is a necessity. The problem of creating a seal is particularly critical at two different points. Principally a seal must be formed between the side walls of the gas hood and the sintering band. Although in existing sintering machines a seal of this kind is usually provided, the result is nevertheless not very satisfactory. Especially if the gaseous atmosphere under the hood is at a pressure considerably elevated above or reduced below the surrounding atmosphere and/ or if the operating temperatures are very high, the seals hitherto used were not suificiently tight. Nevertheless, the provision of a good seal along the side walls of the hood is of especial importance because leakage there may be very much greater than at other points, notably at the charging and delivery ends of the band.

The objects of this invention are to produce a simple and effective manner of sealing the space between a sintering band and the gas hood covering the band.

The means by which the objects are obtained are described more fully with reference to the accompanying diagrammatic drawings in which:

FIGURE 1 is a cross-sectional view through a prior art sintering apparatus showing the seal between the hood and the sintering band;

FIGURE 2 is a similar cross-sectional view showing one of the seals of this invention; and

FIGURE 3 is a longitudinal view of a sintering apparatus of this invention having seals at the entry and delivery ends of the band, and a seal intermediate thereof.

The best of the seals hitherto used, based upon the principle of the labyrinth seal, is a form of construction shown in FIGURE 1 in which the edge of the hood 1 is formed with recesses 2 which are slidably engaged by the side walls 3 of the grate pallet. In order to protect the side walls from being excessively heated, a protective lining 6 of an inert material, usually the previously produced end product of the process being performed, is provided between the charge on the grate 4 and each wall 3. The assembly of a plurality of pans or grate pallets constitutes a moving grate or sintering band upon which is laid a bed or charge 5 of the material being sintered.

This form of a seal has the disadvantage in that it is not entirely tight, even under the most favorable circumstances, because the inside edge 7 of the gas hood does not project into the actual lining 6 and at best is in slidable engagement with the upper edge of the same. The efficiency of the seal primarily relies on the labyrinth effect of the recess to stop gas flow due to the gas pressure differentials created by wind boxes 8. It is imice possible to arrange for the inside edge 7 to project into the lining 6 because, in course of time, the originally granular and loose material of the lining cannot be pre vented from sintering together in practice. It the inner edge 7 were contrived to project downwards into the lining 6, the resistance would be so high as to fracture the edge.

Moreover, in many processes, the volume of the charge is known to shrink so that the gap between the lining 6 and the inside edge 7 then tends to increase thereby reducing the effect of the seal. Since for the performance of reactions at high temperatures the hood 1 must consist of a ceramic material, it is also impossible to increase the dimensions of the recess 2 beyond a certain depth and this is another factor that imposes practical limits upon the efficiency of the seal.

The problem of sealing the other points hereinbefore referred to, namely the entry and discharging ends of the chain, has been even less satisfactorily solved. Insofar as attempts have been made at all to provide a seal at these poitns, recourse has been had to the provision of chain curtains, hinged flaps, and like devices, which naturally form extremely inadequate seals.

The present invention aims at providing a satisfactory solution of the problem of sealing the sintering band on all sides.

According to the invention, the seal along the lateral walls is created by providing the hood with an apron which extends to a substantial extent into pockets filled with a fiowable granular material and protected from the effect of the heat of the charge on the grate.

As shown in FIGURE 2, an apron 9 is securely affixed to each lower edge of the hood 1. Since this is not to be exposed to high temperatures, said apron may consist of a light material such as sheet iron. The side walls of the sintering band are double walls and form pockets 10. Each apron projects into its pocket 10 to a depth depending upon the tightness of the seal, it is desired to create. The pocket 10 is filled with a fiowable solid granular sealing material, such as a finely grained sand, the end product of the process that is being performed, or the fine portion thereof. Lining 6 protects the pocket 10 from the heat of the charge on the sintering band.

It the pocket 10 is filled with the product of the process, preferably the fine portion of the product, then this may be conveniently allowed to be pushed out of the pocket at the delivery end of the band together with the processed product, and may be continuously refilled into the pocket at the entry end.

The efliciency of the seal depends, on the one hand, upon the depth of penetration of the apron into the filling and, on the other hand, upon the fineness of the grain of the filling material. For example, if the pockets are filled with the fine grained (O to 4 mm.) portion of the output product of the sintering process, a depth of penetration of the apron of about 50 mm. will usually be sufficient to maintain a maximum pressure drop of 1 mm. water relative to the outsdie atmosphere.

The excellent sealing efiiciency thus achieved at the side walls is in many cases sufiicient, even in combination with the imperfect seals at the charging and delivery end of the chain, to retain the pressure of the atmosphere under the hood.

However, according to a development of the invention, steps are taken at the same time to improve the seal at the entry and delivery ends of the band. This special arrangement of this invention is shown in FIGURE 3 and is described with reference thereto, with the assumption that several compartments under hoods 1 and 1a, respectively, with diiferent atmospheres and gas pressures 3 are established and sealed from each other and from the surrounding atmosphere.

To this end, additional hoppers 11 and 11a are arranged at the points where the seals are to be established, the discharge end of the hoppers being located close above the surface of the processed bed on the sintering band. A quantity of flowable granular material sufficient to establish a satisfactory seal is then continuously introduced through hoppers 11 and 11a. Preferably the hoppers are filled with the end product derived from the process. However, some other material can likewise be used provided its presence in the final product is not objectionable or its subsequent separation is not difficult. The charging end of the band is similarly sealed by means of a similar hopper 12, but at this end the material delivered through the hopper is the raw material that is to be processed. The material flowing from each hopper forms a gas impervious column up from the surface of the sintering band or the bed of the material thereon and thus effectively seals the charging and delivery ends of the band, and the compartments from each other. However, if in special circumstances, for instance when processing green pellets which cannot be fed through a conventional hopper, the crude charge must be introduced by some other feed means, such as a counter-travelling conveyor belt, then a separate hopper 12 may be provided adjacent the feed end for discharging some alternative material, such as for example the fine portion of the final product of the process that is being performed. The seal created by the material columns 13, 13a and 14 in hoppers 11, 11a and 12, respectively, will naturally be the more eflective the wider the cross section 15, 15a and 16 of the base of the hopper over the charge. x

The provision of sealing means in accordance with the invention is especially useful in processes in which chemically active gases are passed through the bed on the grate, as described for instance in our Patent No. 2,819,539, or in which it is an advantage to adjust and maintain an accurate pressure above or below atmospheric under the hood, or in which the final gas is desired to contain a certain component in maximum concentration and any entry of air through the hood is undesirable, as in the case for example, in the pressure sintering of lead ores. Also, in the treatment of cement clinker to produce white cement, it is quite necessary to limit very closely the gas temperatures and pressures for controlling the extent to which a first oxidation and a following reduction of the clinker proceeds. At the same time, the process must be sealed against the entry of atmospheric air as the presence of as little as 0.1% of air will ruin the white cement.

Having now described the means by which the objects of the invention are obtained.

We claim:

In a sintering apparatus having a sintering band movable beneath and in edge sealed engagement with a gas hood and said band carrying a bed of material to be sintered, the improvement comprising in combination therewith hoppers at the entry and delivery ends, respectively, of the hood, said hoppers extending in sealing contact with the ends of the hood and down to adjacent the surface of the band, at least one additional hopper intermediate said entry and delivery hoppers and separating said hood into compartments, wind boxes beneath said band corresponding in length to said compartments, respectively, and flowable granular material in said hoppers and forming gas seal columns of granular material down through said hoppers onto the surface of and entirely across the surface of said bed of material on said band so that said compartments are gaseously isolated from each other.

References Cited in the file of this patent UNITED STATES PATENTS 1,468,206 Klugh Sept. 18, 1923 1,896,884 Cooper et al Feb. 7, 1933 1,926,032 Bunce Sept. 12, 1933 2,821,469 Davis Jan. 28, 1958 2,832,584 Plonte Apr. 29 1958 2,878,009 Bailey et al Mar. 17, 1959 FOREIGN PATENTS 40,384 Denmark July 1, 1929 524,970 Great Britain Aug. 19, 1940 782,532 Great Britain Sept. 11, 1957 

